Insertion of carbon dioxide and isocyanide into tantalum-amide and tantalum-methyl bonds

The methyl–amide complex [TaCp*(NtBu)Me(NMe2)] (1a) was isolated by reaction of the chloro–methyl [TaCp*(NtBu)MeCl] complex with LiNMe2. Reaction of the mono-amide compounds [TaCp*(NtBu)XY] (X=NMe2, Y=Me (1a); X=NHtBu, Y=Me (1b), Cl (1c)) with CO2 gives the η2-carbamate derivatives [TaCp*(NtBu)(η2-O2CX)Y] (X=NMe2, Y=Me (2a); X=NHtBu, Y=Me (2b), Cl (2c)). A similar reaction with the di-amide complex [TaCp*(NtBu)(NHtBu)2] (1d) gives the di-carbamate derivative [TaCp*(NtBu){η2-O2C(NHtBu)}{η1-O2C(NHtBu)] (2d). Reaction of the methyl–carbamate (2a) with isocyanide CNAr (Ar=2,6-Me2C6H3) gives the η2-iminoacyl–η1-carbamate complex [TaCp*(NtBu){η2-C(Me)NAr}{η1-O2C(NMe2)] (3a). Formation of the related compound [TaCp*(NtBu){η2-C(Me)NAr}{η1-O2C(NHtBu)}] (3b) was only detected by NMR spectroscopy in C6D6 or CDCl3 whereas the reaction of 2b in hexane gives the η1-iminoacyl–η2-carbamate complex [TaCp*(NtBu){η1-C(Me)NAr}{η2-O2C(NHtBu)}] (3b′). All of the new compounds were characterized by elemental analysis and 1H- and 13C-NMR spectroscopy

Oxo and imido/imido exchange and C-H activation reactions based on pentamethylcylopentadienyl imido tantalum complexes

Reactions of [TaCp*Cl4] with two, three and four equivalents of LiNHt Bu give the halo- and amido-imido complexes [TaCp*Cl2(Nt Bu)] (1a), [TaCp*Cl(Nt Bu)(NHt Bu)] (2) and [TaCp*(Nt Bu)(NHt Bu)2] (3), respectively. The related complex [TaCp*Cl2{N(2,6-Me2C6H3)}] (1b) is prepared by a similar reaction using two equivalents of Li[NH(2,6-Me2C6H3)]. Complex 3 can be transformed into 2 and further into 1a by reaction with SiClMe3. Complex 1a reacts with CNt Bu to give the 18-electron adduct [TaCp*Cl2(Nt Bu)(CNt Bu)] (4) whereas addition of excess CN(2,6-Me2C6H3) results in reductive elimination of the carbodiimide t BuN C N(2,6-Me2C6H3) (5) to give [TaCp*Cl2{CN(2,6-Me2C6H3)}3]. However complex 1b does not react with any of the isocyanide ligands. Both complexes 1a and 1b react with PhCHO undergoing imido/oxo exchange to give the imines PhCH NR (R=t Bu, 2,6-Me2C6H3 (6)) and dimeric [TaCp*Cl2(O)]2 or trimeric [(TaCp*Cl)3(m2-Cl)(m2-O)3(m3-O)] oxo-complexes, whereas only 1a reacts with CO2, PhCH NR% (R%=Ph, Me) and (2,6-Me2C6H3)N C Nt Bu producing t BuN CO, PhCH Nt Bu and t BuN C Nt Bu, respectively and the corresponding oxo or imido tantalum derivative. None of the complexes reacts with CO or NCR (R=Me, Ph). The complex [TaCp*Me(Nt Bu)(NHt Bu)] activates C–H bonds when heated in benzene and toluene affording [TaCp*Ph(Nt Bu)(NHt Bu)] (7) and a mixture of [TaCp*(m-MeC6H4)(Nt Bu)(NHt Bu)] 8a and [TaCp*(pMeC6H4)(Nt Bu)(NHt Bu)] (8b). All of the reported organic compounds and tantalum complexes were characterized by 1 H- and 13C-NMR spectroscopyThe authors acknowledge DGICYT (project PB97-0776) for financial support and J.S.N. acknowledges MEC for a fellowship

Synthesis and reactivity of imido niobium complexes containing the functionalized (dichloromethylsilyl)cyclopentadienyl ligand

The niobium complex [NbCpClCl4] (CpCldouble bond; length as m-dashη5-C5H4(SiCl2Me)) (1) with a functionalized (dichloromethylsilyl)cyclopentadienyl ligand was isolated by the reaction of [NbCl5] with C5H4(SiCl2Me)(SiMe3). Complex 1 was a precursor for the imido silylamido derivative [NbCpNCl2(NtBu)] (CpNdouble bond; length as m-dashη5-C5H4[SiClMe(NHtBu)]) (2) after addition of LiNHtBu, which subsequently gave the dichlorosilyl compound [NbCpClCl2(NtBu)] (3) when reacted with SiCl3Me. Addition of LiNHtBu to complex 2 gave the niobium amido complex [NbCpNCl(NHtBu)(NtBu)] (4), which slowly evolved with exchange of the niobium-amido and the silicon-chloro groups to give the dichloroniobium complex [NbCpNNCl2(NtBu)] (CpNNdouble bond; length as m-dashη5-C5H4[SiMe(NHtBu)2]) (5). Reaction of 2 with excess LiNHtBu gave the silyl-η-amido constrained geometry complexes [Nb{η5-C5H4[SiMe(NHtBu)(-η-NtBu)]}(NHtBu)(NtBu)] (6) and [Nb{η5-C5H4[SiClMe(-η-NtBu)]}(NHtBu)(NtBu)] (7), whereas addition of one equimolecular amount of LiNHtBu to 5 in C6D6 afforded complex [NbCpNNCl(NHtBu)(NtBu)] (8). All of the new complexes were characterized by 1H, 13C and 29Si NMR spectroscopy.Universidad de Alcal

Prevalencia y riesgo anual de infeccion por tuberculosis en la población escolar de 7 años de edad de Ceuta

ResumenObjetivoConocer la prevalencia de la infección tuberculosa y el riesgo anual de infección en la población escolar de Ceuta.MétodoEstudio transversal. Se realizó la prueba de la tuberculina (2UT RT-23 Tween 80) a los niños de 7 años de edad escolarizados en Ceuta en 2008. Se consideraron positivos los niños no vacunados con una induración ≥5mm a las 72 horas.ResultadosSe estudiaron 612 niños. La prevalencia de la infección fue del 0,98% (intervalo de confianza del 95%, margen de error del 2,5%). Su distribución mostró diferencias entre las tres zonas de salud, y fue mayor en las zonas más deprimidas, donde llegó al 2,07%. El riesgo anual de infección fue del 0,15%.ConclusionesLa prevalencia de la infección es de las más altas de España, según los últimos estudios realizados. Los resultados no se corresponden con los datos epidemiológicos de tuberculosis de Ceuta, al tener en cuenta los casos importados.AbstractObjectiveTo determine the prevalence of tuberculosis infection and annual risk of infection in the school population of Ceuta.MethodA cross-sectional study was conducted. A tuberculin test (2UT RT-23 Tween 80) was given to 7-year-old schoolchildren in Ceuta in 2008. A positive result was considered as an induration of ≥5mm at 72hours in unvaccinated children.ResultsA total of 612 children were studied. The prevalence of tuberculosis infection was 0.98% (95% confidence interval with a 2.5% margin of error). The distribution showed differences among three health areas, and was greatest in the most deprived area (2.07%). The annual risk of infection was 0.15%.ConclusionsAccording to the most recent studies, the prevalence of tuberculosis infection in Ceuta is one of the highest of Spain. Our results do not agree with the epidemiological data for tuberculosis in Ceuta, which also includes imported cases

Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes

The dinuclear dialkoxo-bridged complexes [(TiCl)2(μ-O2L)(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (O2L = 1,2-O2C2H41a, 1,2-O2C6H41b, 1,2-(OCH2)2C6H41c, O2SiPh21d) were obtained by reaction of [(TiCl2)2(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (A) with the corresponding dilithium salt (1a) or diol (1b, 1c, 1d). Alkylation of 1a and 1b with ClRMg afforded [(TiR)2(μ-O2L)(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (O2L = 1,2-O2C2H4, R = Me 2a, Bz 3a; O2L = 1,2-O2C6H4, R = Me 2b, Bz 3b). Addition of four equiv. of LiOiPr to A afforded [{Ti(OiPr)2}2(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (4). Reaction of 1a with Al(C6F5)3 produced the elimination of the dialkoxo ligand to give [{TiCl(C6F5)}2(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (5), whereas the same reaction of 1b with Al(C6F5)3 produced the oxo-alane adduct [(TiCl)2(μ-O2L)(μ-{(η5-C5Me4SiMeO)2(μ-O·Al{C6F5}3)})] (O2L = 1,2-O2C6H46) which was further transformed to give a mixture of 5 and [(TiCl){Ti(C6F5)}(μ-O2L)(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (O2L = 1,2-O2C6H47). One benzyl group of complexes 3 was abstracted with E(C6F5)3 (E = B, Al) to give the monoionic compounds [Ti(TiBz)(μ-O2L)(μ-{(η5-C5Me4SiMeO)2(μ-O)})][BzE(C6F5)3] (O2L = 1,2-O2C2H4, E = B 8B, Al 8Al; O2L = 1,2-O2C6H4, E = B 9B), although 8Al was unstable in CD2Cl2 evolving to a mixture of compounds where [(TiBz)2(μ-Cl)(μ-{(η5-C5Me4SiMeO)2(μ-O)})][BzAl(C6F5)3] (10) was identified, and compound 9B was also unstable at ambient temperature. Polymerization of ε-caprolactone was only achieved with the tetraalkoxo compound 4. All of these complexes were characterized by NMR spectroscopy and 1a, 1b and 7 by X-ray diffraction studies

Functionalization of silica with amine and ammonium alkyl chains, dendrons and dendrimers: Synthesis and antibacterial properties

Materials modified with ammonium groups on the surface have shown antibacterial activity. In this paper, alkyl chains, carbosilane (CBS) dendrimers and dendrons and poly(amidoamine) (PAMAM) dendrimers containing amine and ammonium groups have been grafted to silica surface and the influence of molecule structure on the stability and on antibacterial activity have been evaluated. These materials have been characterized by thermogravimetric analysis (TGA), zeta (Z) potential, scanning electron microscopy (SEM), infrared spectroscopy (IR) and nuclear magnetic resonance (C-13 CP MAS NMR). The degree of silica functionalization depends on type of outer groups, amine or ammonium, type and core of dendrimer, and length of chains. The Z potential measurements of these materials in water suspensions were used to test their stability in this medium. These measurements showed, for some of the modified silicas, the diminishing of Z potential from positive values toward zero, probably due to interaction of the functional groups with the silica surface. This variation was also dependent on ligand structure and peripheral functions. Finally, studies of inhibition of bacteria growth stand out again the relevance of ligand structure and number of functional groups on silica surface. The most active systems were those with more surface covered, those with cationic groups further away from silica surface and higher dendritic generation.Universidad de AlcaláMinisterio de Economía, Industria y CompetitividadComunidad de Madri

Aryl-imido niobium complexes with chloro-silyl and aryl-η-amidosilyl cyclopentadienyl ligands: X-ray structure of the constrained-geometry compound [Nb(η5-C5H4SiMe2-η1-NAr)(NAr)Cl](Ar=2,6-Me2C6H3)

Reactions of the magnesium imides [Mg(NAr)(THF)]6 (Ar = 2,6-Me2C6H3, 1a; Ph, 1b) with [NbCpClCl4] (CpCl = η5-C5H4(SiMe2Cl)) afforded the imido complexes [NbCpClCl2(NAr)] (Ar = 2,6-Me2C6H3, 2a; Ph, 2b) in good yield. Compound 2a reacted with excess LiNH(2,6-Me2C6H3) to give the silyl-η-amido complex [Nb(η5-C5H4SiMe2-η1-NAr)Cl(NAr)] (Ar = 2,6-Me2C6H3, 3a). Hydrolysis of the Si–Cl bond of compounds 2a and 2b yielded the dinuclear complexes [{NbCl2(NAr)}2{(η5-C5H4SiMe2)2(μ-O)}] (Ar = 2,6-Me2C6H3, 4a; Ph, 4b), respectively. All of the new compounds reported were characterized by NMR spectroscopy and the molecular structure of 3a was determined by X-ray diffraction methods.We gratefully acknowledge the Ministerio de Educación y Ciencia (Project MAT2004-02614) and\ud DGUI-Comunidad de Madrid (Project GR/MAT/0622/2004) (Spain) for financial support. R.A.-M. acknowledges MCyT for a fellowshi

Synthesis and reactivity of oxametallacyclic niobium compounds by using α,ß-unsaturated carbonyl ligands

Reduction of mono(cyclopentadienyl)niobium complexes\ud [NbCpRCl4] [CpR = C5Me4H (1), C5H4SiMe2Cl (2),\ud C5H4SiMe3 (3)] with Na/Hg in the presence of methyl methacrylate\ud [MMA, CH2=C(Me)C(O)OMe (a)], methyl acrylate\ud [MA, CH2=CHC(O)OMe (b)] and mesityl oxide [MO,\ud CMe2=CHC(O)Me (c)] afforded the corresponding derivatives\ud [NbCpRCl2(LL)] [CpR = C5Me4H, LL = MMA (1a); CpR\ud = C5H4SiMe2Cl, LL = MMA (2a), MA (2b), MO (2c); CpR =\ud C5H4SiMe3, LL = MMA (3a), MA (3b)] in variable yields depending\ud on both the cyclopentadienyl and the ¿,ß-unsaturated\ud carbonyl compounds. The reactivity of these complexes\ud was studied toward protic and Lewis acids. Addition of triflic\ud acid TfOH (Tf = CF3SO2) to 3b gave the triflate complex\ud [NbCpRCl2{(CH2)2C(O)OMe}(OTf)] [CpR = C5H4SiMe3 (4)].\ud The Lewis acids E(C6F5)3 (E = B, Al) reacted with complexes\ud Introduction\ud The bonding interaction of a butadiene ligand with a\ud metal center is clearly dependent on the metal atom and\ud may be formulated as a system containing a dianionic ligand\ud for early high-valent transition metals or as a neutral\ud ligand for low-valent late transition metals. However, the\ud stability of the formal oxidation state of the metal atom and\ud the nature of the ancillary substituents of both the complex\ud and the diene ligand could play an important role in defining\ud this interaction. Hence, complexes with this type of ligand\ud are better represented with contributions from two\ud main canonical forms, ¿2,¿-metallacyclic or ¿2-butadiene\ud (Figure 1).[1¿5]\ud [a] Departamento de Química Inorgánica, Universidad de Alcalá,\ud Campus Universitario,\ud 28871 Alcalá de Henares (Madrid), Spain\ud Fax: 34-91-885-4683\ud E-mail: [email protected]\ud [¿] X-ray diffraction studies\ud Supporting information for this article is available on the\ud WWW under http://www.eurjic.org/ or from the author.\ud Eur. J. Inorg. Chem. 2008, 2313¿2320 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2313\ud 2b and 3b to give the three-membered metallacyclic (or ¿2-\ud enone) compounds [NbCpRCl2{¿2-CH2=CHC(OMe){O·\ud E(C6F5)3}}] [CpR = C5H4SiMe2Cl, E = B (5), Al (6); CpR =\ud C5H4SiMe3, E = B (7), Al (8)], which decomposed to the corresponding\ud adducts MA·E(C6F5)3. The same reaction with the\ud 2a and 3a derivatives only allowed the observation of the\ud corresponding adducts MMA·E(C6F5)3. Complexes 2a,b and\ud 3a,b reacted with CO with elimination of the acrylate compounds,\ud MA and MMA, respectively, to give the carbonylniobium(\ud III) compounds [NbCpRCl2(CO)2]2 [CpR = C5H4Si-\ud Me2Cl (9), C5H4SiMe3 (10)]. Analogous reactions with CNAr\ud showed the elimination of the free MA and MMA compounds.We gratefully acknowledge the Ministerio de Educación y Ciencia\ud (MEC) (project MAT2007-60997) and the Dirección General de\ud Universidades e Investigación (DGUI) – Comunidad de Madrid\ud (programme S-0505/PPQ-0328 COMAL-CM) (Spain) for financial\ud support. R. A. A.-M. acknowledges MEC for a fellowship

Whipping of electrified liquid jets

Weapply an electric field to amoderately conducting liquid surrounded by another coflowing liquid, all inside a glass-based microfluidic device, to study nonaxisymmetric instabilities.Wefind that the bending of the electrified jet results in a steady-state, helicoidal structure with a constant opening angle. Remarkably, the characteristic phase speed of the helicoidalwave only depends on the charge carried by the jet in the helicoidal region and its stability critically depends on the properties of the coflowing liquid. In fact, the steady-state helical structure becomes chaotic when the longest characteristic time is that of the inner liquid rather than that of the outer coflowing liquid. We also perform a numerical analysis to show that the natural preference of the jet is to adopt the conical helix structure observed experimentally

Bacteria capture with magnetic nanoparticles modified with cationic carbosilane dendritic systems

Bacteria elimination from water sources is key to obtain drinkable water. Hence, the design of systems with ability to interact with bacteria and remove them from water is an attractive proposal. A diversity of polycationic macromolecules has shown bactericide properties, due to interactions with bacteria membranes. In this work, we have grafted cationic carbosilane (CBS) dendrons and dendrimers on the surface of iron oxide magnetic nanoparticles (MNP), leading to NP (ca. 10 nm) that interact with bacteria by covering bacteria membrane. Application of an external magnetic field removes MNP from solution sweeping bacteria attached to them. The interaction of the MNP with Gram-positive S. aureus bacteria is more sensible to the size of dendritic system covering the MNP, whereas interaction with Gramnegative E. coli bacteria is more sensible to the density of cationic groups. Over 500 ppm of NPM, MNP covered with dendrons captured over 90% of both type of bacteria, whereas MNP covered with dendrimers were only able to capture S. aureus bacteria (over 90%) but not E. coli bacteria. Modified MNP were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), Z potential and dynamic light scattering (DLS). Interaction with bacteria was analyzed by UV, TEM and scanning electron microscopy (SEM). Moreover, the possibility to recycle cationic dendronized MNP was explored.Ministerio de Economía, Industria y CompetitividadComunidad de MadridInstituto Ramón y Cajal de Investigación Sanitari